1) Field of the Invention
The present invention relates to a turbine rotor blade that can prevent flow separation in a trailing edge portion of the rotor blade and can prevent a loss of flow from being increased.
2) Description of the Related Art
FIG. 7 and FIG. 8 are cross sectional views of a conventional turbine rotor blade, FIGS. 9A and 9B are cross sectional views of the rotor blade shown in FIG. 7 or FIG. 8 in a cross section along a line D—D, and FIG. 10A is a schematic view of a conventional blade surface velocity and FIG. 10B is a schematic view of a separation state of the flow based on a blade shape. FIG. 7 shows a case that a trailing edge of the rotor blade is formed in a parabolic shape, and this case is disclosed by the applicant of the present invention in Japanese Utility Model No. 2599250. Further, FIG. 8 shows a case that the trailing edge of the rotor blade is formed in a linear shape.
As shown in FIG. 7 to FIG. 9A and FIG. 9B, a plurality of rotor blades 2 provided radially in a circumferential direction of a boss 1 are formed so that a blade thickness t becomes gradually thinner toward a trailing edge 3 of the rotor blade. Since the thickness t of a part just before being thin is generally set to a maximum blade thickness in many cases, this part is called a maximum blade thickness portion and a downstream side of the maximum blade thickness portion 4 is called a trailing edge portion 5, for convenience in explanation.
There are assumed an extension line 6a of a suction surface 6 in an upstream side of the maximum blade thickness portion 4, an extension line 7a of a pressure surface 7 in the upstream side of the maximum blade thickness portion 4, and a center line 8 of the blade thickness t. At this time, the trailing edge 3 of the trailing edge portion 5 based on the conventional technology is designed to be positioned on the center line 8.
A cross section near the trailing edge portion 5 is formed in the manner mentioned above because the blade shape is conventionally planned based on the center line 8, and the blade thickness t is set in such a manner that the blade thickness t is divided into the suction surface 6 and the pressure surface 7 by one half in a perpendicular direction with respect to the center line 8.
However, in the conventional turbine rotor blade, the trailing edge 3 is formed in the manner mentioned above, and therefore a suction surface velocity 9 in a main stream generates a rapid ascent portion 11 due to a rapid increase of a deflection angle θ of flow in the downstream side of the maximum blade thickness portion 4, and generates a rapid deceleration portion 12 running into the trailing edge 3, as shown in FIG. 10A and FIG. 10B. Accordingly, there has been a problem that a separation portion 13 of the flow occurs in the trailing edge portion 5 of the suction surface 6, and a loss of flow is increased.